Coaxial transmission line termination



Aug. 30. 1966 G, R. TAHARA ETAL 3,270,230

, COAXIAL TRANSMISSION LINE TERMINATION Filed Oct. 18, 1962 ZSheets-Sheet 1 FIG.

INVENTORS GUY K. PATTERSON and GORO R. TAHARA BY Mix/Q 0m ATTORNEY Aug.30. 1966 5, R. TAHARA ETAL 3,270,280

COAXIAL TRANSMISSION LINE TERMINATION Sheets-Sheet .2

Filed Oct. 18, 1962 INVENTORS GUY K. PATTERSON and GORO R. TAHARA BYATTORNEY Aug. 30. 1966 R. TAHARA ETAL 3,270,280

COAXIAL TRANSMISSION LINE TERMINATION Filed Oct. 18. 1962 5 Sheets-Sheet5 FIG. 3-

lNVENTORS GUY K. PATTERSON and GORO R. TAHARA BY NJNQBQLQW ATTORNEYUnited States Patent 3,270,280 CUAXHAL TRANM1S1ON LHNE TERMHNATHON GoreR. Tahara, Sunnyvale, and Guy 1i. Patterson, Menlo Park, Calif,assignors to Fhilco Corporation, Philadelphia, Fa, a corporation ofDelaware Filed Get. 13, 1962, Ser. No. 231,455 5 Claims. (Cl. 32495)This invention relates to a coaxial transmission line termination, andmore particularly to a power absorbing load for the termination of highfrequency coaxial transmission lines Often it is desirable to dissipatehigh frequency energy in a load to prevent the radiation of the energy,the radiant energy being converted to heat energy in the load. Loads forthe dissipation of high frequency energy are well known and ofteninclude an inner conductor structure comprising an elongated resistorand an outer conductor structure comprising a tapered sleeve surroundingthe resistor and connected thereto at one end thereof. When air is usedas the dielectric medium between the inner and outer conductorstructures, such load devices are capable of dissipating only relativelysmall amounts of power. When greater radio frequency power must bedissipated, such loads are provided with forced air cooling, or a liquiddielectric is employed to replace the air dielectric. Also, auxiliaryrefrigerating means are often employed to cool the dielectric liquidwhen it is desired to handle large radio frequency power. Althoughnumerous schemes have been proposed for cooling such loads, theygenerally increase in complexity and cost as the amount of energy to bedissipated increases.

A load construction providing good natural convection cooling of theload resistor employed therein is shown in US. Patent 2,901,710 to E.Garthwaite. The load device shown in the patent includes an elongatedresistor as the inner conductor and a pair of convergent plates disposedon opposite sides of the resistor as the outer conductor structure. Theconvergent ends of the plates are connected to one end of the resistor,and means are provided for applying high frequency energy to bedissipated between the other end of the resistor and the divergent endsof the plates. When the load is arranged with the plates positionedvertically, excellent natural convection cooling of the resistorpositioned between the plates is provided. In order to handle highpower, such units may be built with a large resistor. However, thelarger the diameter of the resistor, the greater must be the spacingbetween the convergent plates of the outer conductor structure, wherebythe size of the load is increased.

It is well known that by measuring the voltage across a portion of theresistor included as the inner conductor of a coaxial transmission linetermination, an indication of the power dissipated by the termination isobtained. Often, a crystal diode is employed to convert the voltage toDC. for convenient measurement by an indicating instrument having ascale calibrated in watts or power. Crystal diodes, however, have anoperating temperature range within which they operate accurately. Atoperation above the upper temperature limit the diode may burn out orfunction improperly, and for accurate wattmeter readings this limit mustnot be exceeded.

An object of this invention is the provision of means for greatlyincreasing the heat dissipating capability of a coaxial transmissionline termination without increasing the over-all dimensions of such atermination.

An object of this invention is the provision of a coaxial transmissionline termination of relatively simple construction and having high powerhand-ling capabilities.

An object of this invention is the provision of a watt- 3,27%,230atented August 30, 1966 meter which includes a heat dissipatingtermination and crystal diode, said diode being located at a relativelycool location on the termination whereby large power measurements may bemade without overheating the diode.

These and other objects and advantages of the invention are achieved bymeans of a load construction including a pair of convergent plates asthe outer conductor structure and a plurality of parallel connectedelongated resistors as the inner conductor structure. The resistors arelocated one above the other and, when the load is used as a wattmeter, adiode holder is secured to the lower-most resistor. Since the heat fromthe resistors rises by convection of cooling fluid, such as air, theheat from the resistors above the lower-most resistor contribute littleto the temperature rise of the diode. Further, by mounting the resistorsin a divergent manner, a maximum physical separation of the diode fromthe upper resistors is obtained.

In the drawings, wherein like reference characters refer to the sameparts in the several views:

FIGURE 1 is a top view of a termination embodying this invention;

FIGURE 2 is a side elevational view of the termination shown in FIGURE1, with parts shown broken away for clarity; and

FIGURE 3 is an enlarged fragmentary sectional view through the diodeholder showing the manner in which it is mounted on the termination.

Referring to FIGURES 1 and 2 of the drawings, the termination of thisinvention comprises a pair of elongated tubular film-type load resistorsof identical construction, It) and 11, disposed between a pair ofconvergent plates, or slab lines 13 and 14, also of identicalconstruction. Resistors 10 and 11 comprise the inner conductor structureof the load, and plates 13 and 14 comprise the outer conductor structurethereof. The convergent ends of the plates 13 and 14 are connected toterminals of resistors 10 and 11 by means of rear contact plateassemblies 16 and 16' of identical construction. When the termination isused in a Wattmeter arrangement a diode holder 15 is secured to thelower contact plate assembly 16' in a manner shown in FIGURE 3 anddescribed in detail hereinbelow.

The divergent front ends of plates 13 and 14 are secured by screwfastening means 17 to the vertical side walls of a front end connectorbody 18. A line connector member 19 engages the tapped portion of athrough hole 21 formed in the connector body, and together with theconnector body provides an electrical connection between an attachingcollar of a coaxial line, not shown, and the outer conductor structure13, 14 of the termination.

A tapered inner connector 22, coaxially disposed within the connectormember 19 and electrically insulated therefrom by a suitable dielectricsleeve, conductively connects to a generally cylindrical brass pin 23formed with an integral axial flange 241 which extends over the innerconnector 22 in good electrical connection therewith. A dielectricbushing 26 is positioned in the space between the pin 23 and theconnector body 18 and extends inwardly from the connector body 18. Asetscrew 27 (FIG. 1) fixedly secures the bushing within the connectorbody 18.

The rear end of bushing 26 is preferably formed with a vertical recess28 which extends the entire height thereof and within which ispositioned a contact mounting plate 2%. The reduced diameter rear end ofthe pin 23 extends into a hole formed in the center of the contactmounting plate 29 and is suitably connected thereto by soft soldering orthe like.

The rear end of the contact mounting plate is provided with a pair ofintersecting surfaces extending at an angle of slightly less than 90with the axis 31 of the load device. A pair of identically constructedinput connector contacts 32, 33 are secured to said contact mountingplate, the input connector contacts being provided with generallyforwardly extending pins 34 and 36 which engage suitable holes formed inthe rearward walls of the contact mounting plate and which are fixedlysecured thereto by soft soldering or the like.

The tubular film-type load resistors and ill each may comprise a glazedcylindrical ceramic tube 41 with a resistor film 42 disposed on theexternal surface thereof. Said film may comprise an alloy including ahighly stable tin oxide deposited on the external surface of the glazedceramic tube which is then fired at a high temperature to disperse theresistance film throughout the body of the glaze. Bands 44 and 44' ofconductive metal, such as silver, are applied to the ends of theresistors and extend over the resistance film in good electrical contacttherewith. It will here be understood that, for purposes of illustrationand clarity, the showing of the resistance film 42 and conductive bands44 and 44' is greatly exaggerated dimensionally in the drawing. Theinput connector contacts 32 and 33 are provided with axially extendingslotted flanges which extend over the conductive bands 44 and aresecured thereto by soldering or other suitable means not shown.

The rear contact plate assemblies 16 and 16', as shown in the drawings,each include a slotted axial flange 47 secured to the silver conductingbands 44' of the resistors 1i) and 11 by a plurality of retaining rings46. Screws 43, extending through holes formed in the outer conductorplates, fixedly secure the rear contact plate assemblies 16 and 16 tothe plates. The outer conductor plates 13 and 14 are spaced apart bymetal spacers 49 of brass or the like secured to the plates by screwfastening means 51. The spacers 49 are of different lengths to providethe proper curvature of the outer conductor plates 13 and 14, and forgood matching of the load to the transmission line the plates areprovided with a substantially exponential curvature.

Resistors 10 and 11 are electrically connected in parallel in the novelarrangement of this invention, the energy from a power source, notshown, entering the device through the line connector 19 and dividingsubstantially equally at said resistors. The two resistors in parallelprovide an increased power dissipating surface over single resistorconstructions for increased power handling capabilities.

The coaxial line termination described in detail above is particularlywell suited for use in making radio frequency power measurements.Reference is now also made to FIGURE 3 of the drawings wherein theconnection of microwave diode holder to the novel coaxial linetermination is shown in detail. Although the diode holder forms no partof the invention, a suitable construction includes a housing 51 havingan axial flange 52 secured by retaining rings 46 to flange 47 on lowerrear contact plate assembly 16'. The housing is capped by a ferrule 53secured thereto by a captive threaded collar 54. A cartridge-type diode56 is coaxially supported in housing 51 by a bushing 57.

A metallic ring or band 58 of silver or the like is applied to resistor11 a spaced distance from the rear end thereof and electrical connectionis made between said band and diode 56; the connection including ametallic band 59 inside the resistor Ill connected to band 53 byconductors 61 extending through axial holes in the resistor. A metallicspider, or disc, 62 engages band 59 and supports one terminal of aharmonic suppression resistor 63. The other terminal of resistor 63 isconnected to a contact pin 64 of diode 56 by means of a sleeve 66. Theother diode. terminal 67 is connected to a radio frequency bypasscapacitor 68 of the disc type and through electrical components, notshown, to a DC. output conductor 69. As is well understood by thoseskilled in this art, the DC. output is directly proportional to thevoltage across the portion of resistor 11 between bands 44' and 58which, in turn, is directly proportional to the power dissipated by thetermination. A flow of cooling fluid such as air through the tubularresistors is made possible by radial holes 71 formed in the flanges ofthe input connector contacts 32 and 33. The rear end of resistor 10 isleft open and radial holes 72 are formed in housing 51 for accommodationof the fiow of air through resistors It) and 11, respectively.

As is well understood, crystal diodes such as diode 56 have atemperature operating range within which they must operate. If thetemperature exceeds the maximum temperature rating the diode eitherburns out or fails to function as predicted. In either case, theaccuracy of the wattmeter is impaired. With the novel terminationconstruction of this invention, the diode is not only mounted adjacentthe inner conductor of the termination, but is also mounted at arelatively cool position. A substantial portion of the heat from upperresistor it) rises by convection of the cooling fluid and therebycontributes little to the rise in temperature of the diode. Sincesubstantially one-half of the total power dissipated by the terminationis dissipated by resistor Jill, it will be apparent that the terminationis capable of handling more power without damaging the diode than woulda termination of similar construction but employing only a singleresistor. In accordance with this invention, the parallel connectedresistors extend in a divergent manner from the front end of the load tothe rear end thereof. By placing the resistors close together at thefront end a minimum mismatch of impedance is experienced at the input tothe resistors. A good impedance match at the input to the resistorswould be diflicult to obtain if the resistors were spread apart asubstantial distance thereat, and for this reason, the resistors arephysically located close together adjacent the input ends. By spacingthe other ends of the resistors apart as illustrated, the diode 56 islocated a maximum distance from the heat-producing resistor iii, andconsequently, the wattmeter is capable of high power measurementswithout damage to the diode. Although the divergent arrangement ofresistors 10 and 11 is not essential to the proper operation of the loaddevice, the large power handling capability is made possible by locatingthe diode 56 below resistor lltl adjacent the end of lower resistor 11.

The invention now having been described in detail in accordance with therequirements of the patent statutes, various changes and modificationswill suggest themselves to those skilled in this art. For example, theinvention is not limited to the use of a pair of resistors, more thantwo resistors may be employed in parallel in accordance with thisinvention, It will be apparent when more resistors are employed, moresurface will be available for the dissipation of heat. With the outerconductor plates, or slab lines, in a generally vertical position asillustrated, air easily circulates by convention past the load resistorsto cool them. If desired, the termination may be supported in a casingcontaining a liquid dielectric as is well understood by those skilled inthis art. -In such an arrangement the flow of fluid such as transformeror mineral oil past the resistors provides for increased cooling action.However, by employing a plurality of resistors, the increased powerhandling capability of the load is made possible without resort toliquid dielectric in many instances. The disadvantages of the use ofliquid dielectric, including the possibility of leakage of thedielectric from the casing or housing is thereby eliminated. It isintended that these and other such changes and modifications shall fallwithin the spirit and scope of the invention as recited in the followingclaims.

We claim:

1. A microwave load for use in energy dissipating or measuring apparatusincluding an inner conductor structure comprising a pair of elongatedresistors electrically connected in parallel, an outer conductorstructure comprising a pair of convergent slab lines disposed onopposite sides of said resistors, said resistors extending in adivergent manner from the divergent to the convergent ends of the slablines, means connecting the convergent ends of said slab lines to oneinterconnection of the said resistors, and means at the divergent endsof said slab lines for connection of a source of microwave energybetween said slab lines and the other interconnection of said resistors.

2. The invention as recited in claim 1 including a diode and terminalmeans therefor to which measuring means may be connected, said diodeconnected adjacent one end of one of said resistors.

3. A microwave load for use in energy dissipating or measuringapparatus, comprising: a pair of convergent plates to be positionedsubstantially vertically; a pair of elongate resistors between saidplates, said resistors being one above the other When said plates aredisposed vertically and extending divergently from the divergent to theconvergent ends of said plates; means for connecting the divergent endsof said plates to the outer conductor of a coaxial line; means forconnecting the convergent ends of said resistors to the inner conductorof a coaxial line; and means connecting the divergent ends of saidresistors to the convergent ends of said plates.

4. Apparatus according to claim 3, further including a diode andterminal means therefor to which measuring means may be connected, saiddiode connected to the lower resistor at the divergent end thereof.

5. Apparatus according to claim 3, wherein the divergent ends of saidplates are secured and electrically connected to a connector body, andthe convergent ends of said resistors are supported by said body but areinsulated therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,399,930 5/1946Keister 333-22 2,524,183 10/1950 Wheeler 324 2,565,900 8/1951 Wiley32495 2,901,710 8/1959 Garthwaite 333-22 3,027,514 3/1962 Bird 324--95WALTER L. CARLSON, Primary Examiner.

R. V. ROLINEC, Assistant Examiner.

1. A MICROWAVE LOAD FOR USE IN ENERGY DISSIPATING OR MEASUREMENTAPPARATUS INCLUDING AN INNER CONDUCTOR STRUCTURE COMPRISING A PAIR OFELONGATED RESISTORS ELECTRICALLY CONNECTED IN PARALLEL, AN OUTERCONDUCTOR STRUCTURE COMPRISING A PAIR OF CONVERGENT SLAB LINES DISPOSEDON OPPOSITE SIDES OF SAID RESISTORS, SAID RESISTOR EXTENDING IN ADIVERGENT MANNER FROM THE DIVERGENT TO THE CONVERGENT ENDS OF THE SLABLINES, MEANS CONNECTING THE CONVERGENT